Magnetic bubble domain devices are well known in the art. There are two basic types of devices depending upon the method by which bubbles are propagated in bubble devices; the first is the field access type and the second is the current (or conductor) access type. The most familiar mode of operating a magnetic bubble device is termed the "field-access" mode. In this mode, a pattern of magnetically soft elements (such as Permalloy or ion implanted contiguous disks) is formed in a plane adjacent a layer of material in which the bubbles are moved. A magnetic field is generated in the plane of the layer and the field caused to reorient to incrementally-offset radial positions cyclically in the plane. Each element is so shaped that various portions thereof respond to in-plane field to generate pole-patterns which change as the field processes. The configuration of adjacent elements sets up a sequence of travelling potential wells in the layer which causes bubble movement.
In current access devices, the necessary potential wells are provided by a set of conductor patterns in which polyphase, usually two or three phase, currents are transmitted. The conductors are typically formed in multiple layers, insulated from one another and driven in a two or three phase manner. An example of such a device is described in U.S. Pat. No. 3,460,116.
Various types of magnetic bubble domain device architectures are known in the prior art, one of the best known being the major loop/minor loop configuration. The major loop/minor loop configuration, such as described in the U.S. Pat. No. 3,618,054, consists of a plurality of first recirculating "minor" channels and a second "major" channel.
Many devices have been proposed in the prior art for generating magnetic bubble domains in a magnetic bubble domain material. These devices can be divided into two classes: those which generate bubble domains by replication from an existing bubble domain, and those which initially nucleate a bubble domain in the magnetic bubble material.
Bubble generation is achieved in permalloy field access bubble devices by first stretching an existing bubble, and then cutting it into two parts, typically so that one part is left in the generator region and the second is transferred to a propagation track to represent data in the device. The bubble stretching is performed either by applying a high current pulse to the same conductor used for cutting the bubble or by utilizing some large size permalloy propagation elements such as the pickax element. The prior art nucleation bubble generators exhibit poor reliability at elevated temperatures because of the multibubble nucleation that takes place along the edges of the conductor loop. Although reliability of generator operation can be improved slightly by using current pulses with long decay time, such generators still are disadvantageous in many applications.
One method of nucleating magnetic bubble domains is described in U.S. Pat. No. 3,662,359, which is hereby incorporated by reference.
In such a configuration, control means are connected to the current source for producing a current pulse at a predetermined instant of the re-orienting magnetic drive field so that a localized magnetic field nucleating a bubble domain is produced at the position of the conductor loop portion.